[CmdPal] Extension Toolkit localization (#40677)

## Summary of the Pull Request
Moves hardcoded string resources from the extension toolkit to a new
`Resources.resx` file.
## PR Checklist
- [x] **Closes:** #40397
- [ ] **Communication:** I've discussed this with core contributors
already. If the work hasn't been agreed, this work might be rejected
- [ ] **Tests:** Added/updated and all pass
- [x] **Localization:** All end-user-facing strings can be localized
- [x] **Dev docs:** No need
- [x] **New binaries:** None
- [x] **Documentation updated:** No need
## Detailed Description of the Pull Request / Additional comments
`Resources.resx` and `Resources.Designer.cs` are located in
`Properties\`, as with other projects.
<!-- Describe how you validated the behavior. Add automated tests
wherever possible, but list manual validation steps taken as well -->
## Validation Steps Performed
Tested locally, strings display correctly

src/modules/cmdpal/extensionsdk/Microsoft.CommandPalette.Extensions.Toolkit/CopyTextCommand.cs

@@ -8,12 +8,12 @@ public partial class CopyTextCommand : InvokableCommand
 {
     public virtual string Text { get; set; }
 
-    public virtual CommandResult Result { get; set; } = CommandResult.ShowToast("Copied to clipboard");
+    public virtual CommandResult Result { get; set; } = CommandResult.ShowToast(Properties.Resources.CopyTextCommand_CopiedToClipboard);
 
     public CopyTextCommand(string text)
     {
         Text = text;
-        Name = "Copy";
+        Name = Properties.Resources.CopyTextCommand_Copy;
         Icon = new IconInfo("\uE8C8");
     }